The present invention relates to the stamping of metal products, and more particularly to deep-drawn stamping.
There is a demand for metallic items or parts that are bullet-shaped and hollow, and that include one or more holes in the normally closed end. For example, one such item is a spark plug ground shield 10 (FIGS. 31-32) incorporated into a spark plug 20 (FIG. 3). The ground shield is essentially bullet-shaped and hollow, having a cylindrical side wall 12 and a strap 14. The strap is integral with the side wall and extends diametrically across the normally closed end of the ground shield 10.
Typically, the ground shield 10 is fabricated by, first, stamping a metal blank into a bullet shape and, second, machining the closed end to create the strap 14 arcing away from the remainder of the piece. This process is undesirably labor-intensive and therefore expensive and prone to quality and consistency issues.
While at first blush, the ground shield 10 appears to be capable of manufacture using deep-drawn stamping exclusively (i.e. no machining), such manufacture is not possible. Specifically if the strap 14 were formed by piercing the piece, the strap could not thereafter be pulled away from, or arced away from, the remainder of the piece because insufficient metal is left in the strap to withstand such forces.